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Rare-Earth Element- and Yttrium-Bearing Pegmatite Dikes Near Dora Bay, Southern Prince of Wales Island

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Rare-Earth Element- and Yttrium-Bearing Pegmatite Dikes Near Dora Bay, Southern Prince of Wales Island RARE-EARTH ELEMENT- AND YTTRIUM-BEARING PEGMATITE DIKES NEAR DORA BAY, SOUTHERN PRINCE OF WALES ISLAND By James C. Barker and Cheryl Mardock * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * OFR 19-90 UNITED STATES DEPARTMENT OF THE INTERIOR Manuel Lujan, Jr., Secretary BUREAU OF MINES T S Ary, Director CONTENTS Page Abstract .......................................................... 1 Introduction ...................................................... 2 Land status and access ............................................ 4 Geologic setting .................................................. 4 Regional geology ................................................ 4 Intrusive rocks ................................................. 4 Pegmatite dikes .................................................. 7 Mineralogy and Petrography of the Pegmatite dikes ................. 8 Sampling methods and analytical techniques ........................ 10 Mineralization .................................................... 10 Resources ......................................................... 20 Heavy mineral survey .............................................. 20 Discussion and conclusions ........................................ 22 References ........................................................ 25 Appendix A. - Rock sample multi-elements analyses ................. 26 Appendix B. - Heavy mineral concentrates multi-element analyses... 35 ILLUSTRATIONS 1. Location of the Dora Bay intrusive complex on southern Prince of Wales Island .............................................. 3 2. Geology, mineralized pegmatite dikes, and sample locations near Dora Bay: Insert shows lateral zoning of REE-Y-Cb with respect to SiO 2 between pegmatites and vein-dikes ............ 5 3. SEM backscatter image of intergrown monazite (bright mineral in center) with thalenite (cream colored mineral on left) and bastnaesite (darker gray minerals) in a matrix of quartz and calcite. Magnification is 200X .......................... 9 4. Location of panned heavy mineral concentrates near Dora Bay... 11 5. Correlation of REE+Y to SiC 2 in mineralized pegmatite dikes... 19 6. Comparison of REE composition of Dora Bay pegmatite dikes to mineral deposits at Bokan Mountain and other major U.S. REE sources ...................................................... 23 TABLES 1. Major oxide analyses and normative mineralogy (in pct) of whole rock samples from the Dora Bay complex .............. 6 2. Principal REE and Cb-bearing minerals identified at Dora Bay.. 8 3. Analytical methods and detection limits ....................... 12 4. Pegmatite dikes and wallrock sample results ................... 13 5. Eudialyte-bearing pegmatite sample results .................... 16 6. Other sample results .......................................... 17 7. Volume and weights of heavy mineral concentrates, and normalized yttrium in panned samples from the Dora Bay area.. 21 i UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT cm centimeter cps count per second ft foot 9 gram in inch lb pound lb/yd 3 pound per cubic yard mg milligram mi mile pct percent ppm part per million ppb part per billion um micrometer, micron st short ton yd3 cubic yard RARE-EARTH ELEMENT AND YTTRIUM-BEARING PEGMATITE DIKES NEAR DORA BAY, SOUTHERN PRINCE OF WALES ISLAND By James C. Barkeri! and Cheryl Mardock2/ ABSTRACT Yttrium and rare-earth element pegmatite dikes are associated with a peralkaline granitic and nephelene syenite complex near Dora Bay on southern Prince of Wales Island. Mineralized dikes were mapped and sampled during USBM investigations in 1987 and 1988. Coarse-grained pegmatite dikes, which emanated as late-stage magmatic fluids from the intrusion, further evolved into vein-dikes and ultimately silica-rich veins. The dikes can be traced up to two miles along a north- south zone. Lithophile elements exhibit a pronounced zonation in vein-dikes and veins that are distal to the Dora Bay complex with increasing values correlating with increasing distance from the complex. The pattern of mineralization suggests very late stage magmatic fluids containing the incompatable lithophile elements were injected into a preexisting north-south fracture zone. REE mineralogy exhibit fine-graired intergrowths of principally thalenite and bastnaesite with lessor monazite and eudialyte. Euxenite contains most of the columbium values and zircon is commonly associated with the dikes. Estimates of inferred and hypothetical resource tonnage range from 1.7 X 106 to 8.5 X 106 st for two deposits. Contained REO (including yttrium) averages 0.5 pct and ranges up to 2.0 pct. Deposits are of polymineralic composition and about half of this resource comprises the heavy yttrium subgroup. 1/Supervisory physical scientist, Alaska Field Operations Center, Fairbanks, Alaska. 2/Geologist, Albany Research Center, Albany, Oregon. 1 INTRODUCTION Southern Prince of Wales Island, in southeast Alaska (fig. 1), is host to a trend of sodium-rich intrusive complexes and associated radioactive mineral occurrences that contain varying amounts of rare-earth elements (REE), columbium (niobium).!/, and other lithophile metals (1, 2)4!. During investigations in 1987 and 1988 by the Bureau of Mines, mineralized showings near Dora Bay were found to be among this trend of occurrences. These studies are being conducted as part of the Bureau's effort to identify and assess Alaskan reserves or resources of certain critical and strategic minerals which could be extracted during periods of prolonged national shortages. On southern Prince of Wales Island, the Bureau has recently conducted other reconnaissance investigations at Stonerock Bay, Mclean Arm, Bokan Mountain, Mcira Sound, and Cholmondeley Sound. 3/The element 'Niobium' is also referred to as 'Columbium' in the context of a commercial commodity. 4/Underlined numbers in parentheses refer to the list of references preceding the appendices at the end of this report. Columbium is used widely as a hardening alloy in high-strength, low-alloy steels. It is considered of strategic importance to the United States (U.S.) because of its application in national defense and petroleum industries, and developing uses in advanced technology. At present the country is entirely reliant on foreign sources of the metal (3). The REE are a group of 15 chemically similar elements consisting of the lanthanide-series, atomic numbers 57 through 71. Yttrium, whose atomic number is 39, is often included with the REE because of similar chemical properties. These elements are often subdivided into two groups: 1) the light REE (cerium subgroup) consists of elements with atomic numbers 57 through 63; and 2) the heavy REE (yttrium subgroup) consists of elements with atomic numbers 39 and 64 through 71. The REE have wide and increasing applications as catalysts for the petrochemical industry, steel alloys, lighting, phosphors, glass and optics, and electronics (4). New alloy compositions for magnets utilizing certain REE have led to improved magnetic field strengths. Recent research in the fields of superconductors and metal-oxide ceramics has been dramatically advanced by the use of various REE compounds, particularly yttrium. At the present time, however, these potential new uses are still in early research and development stages and have not yet resulted in a significant increase in demand for REE. The U.S. is self-reliant in the lighter REE, however, most of the heavy REE, including yttrium are imported. Worldwide, most of the production of the heavy REE occurs as a by-product to tin and titanium placer mining. There has been no previous documented evaluation of the REE or columbium resource potential near Dora Bay. However, of significance is the identification by Herreid and others (5) of eudialyte in zirconium mineralized dike rubble on a beach of Dora Bay. Eudialyte is a zirconium mineral often associated with REE deposits elsewhere in the world. At Dora Bay, Eberlein and others (6) further noted its occurrence in a diorite and syenite intrusion they mapped immediately southwest of Dora Bay. 2 Figure 1. - Location of the Dora Bay intrusive complex on southern Prince of Wales Island. 3 The REE-columbium deposits near Dora Bay described in this report are not of sufficient grade to be presently economic to mine as compared to other deposits in the world. However, much of the world's REE resource potential is comprised of only the lighter REE, whereas most deposits on southern Prince of Wales Island, including those at Dora Bay, also contain the heavy yttrium subgroup. Therefore, the results of the investigation at Dora Bay are presented in the following report. LAND STATUS AND ACCESS The investigation area near Dora Bay lies in the Craig A-1 and A-2 quadrangles and is located in the federally managed Tongass National Forest. Certain land entitlement claims have been made in the vicinity by the SeaAlaska Native Corp. Final disposition of those claims is continuing. Elsewhere the area is designated multiple-use by the Forest Service and is open to mineral entry. Dora Bay is a well-sheltered, relatively deep bay that is readily accessible by either boat or float planes. A foot trail leads from the head of the bay to Dora Lakes where a canoe was used during this project to gain access to areas of interest. During the field examination in 1987-88 on-going logging operations were continuing to expose additional outcrops of bedrock. Logging roads now provide access to the region immediately west of the project area. GEOLOGIC SETTING
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